SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Expires: February 28, 2011 Estimated average burden hours per response 0.5
X	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* LIME ROCK PARTNERS II LP (Last) (First) (Middle) C/O LIME ROCK MANAGEMENT LP 518 RIVERSIDE AVENUE (Street) WESTPORT CT 06880 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol NATCO GROUP INC [ NTG ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 04/07/2006
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock ( 1 )	04/07/2006		S		110,061	D	$25.29	0	D ( 2 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series B Convertible Preferred Stock	$7.805 ( 3 )	04/07/2006		S			15,000	( 4 )	( 4 )	Common Stock	1,921,844	$3,453.473	0	D ( 2 )

1. Name and Address of Reporting Person* LIME ROCK PARTNERS II LP (Last) (First) (Middle) C/O LIME ROCK MANAGEMENT LP 518 RIVERSIDE AVENUE (Street) WESTPORT CT 06880 (City) (State) (Zip)

1. Name and Address of Reporting Person* Lime Rock Partners GP II, L.P. (Last) (First) (Middle) C/O LIME ROCK MANAGEMENT LP 518 RIVERSIDE AVENUE (Street) WESTPORT CT 06880 (City) (State) (Zip)

1. Name and Address of Reporting Person* LRP GP II, Inc. (Last) (First) (Middle) C/O LIME ROCK MANAGEMENT LP 518 RIVERSIDE AVENUE (Street) WESTPORT CT 06880 (City) (State) (Zip)

Explanation of Responses:

1. This Form 4 is filed by Lime Rock Partners II, L.P. ("Fund"), Lime Rock Partners GP II, L.P. ("GP LP"), and LRP GP II, Inc. ("GP Inc.").

2. The Fund is the direct beneficial owner of Issuer's securities. GP LP may be deemed to be an indirect beneficial owner of Issuer's securities because of its position as general partner of the Fund and its entitlement to a share of the Fund's profits, and GP Inc. may be deemed to be an indirect beneficial owner of the Issuer's securities because it is the general partner of GP LP and is entitled to a share of GP LP's profits. GP LP and GP Inc. each disclaim beneficial ownership of these securities and this report shall not be deemed to be an admission that GP LP or GP Inc. is the beneficial owner of such securities.

3. Based on a face value of $1,000 per share of the Series B Convertible Preferred Stock.

4. The Series B convertible preferred stock is convertible into common stock of the Issuer at any time at the option of the holder and has no expiration date.

	LIME ROCK PARTNERS II, L.P., by Lime Rock Partners GP II, L.P., its General Partner, by LRP GP II, Inc., its General Partner By: Mark A. McCall	04/11/2006
	LIME ROCK PARTNERS GP II, L.P., By: LRP GP II, Inc., its General Partner, By: Mark A. McCall	04/11/2006
	LRP GP II, INC. By: Mark A. McCall	04/11/2006
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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